This paper demonstrates that Cu 2 O nanoparticles form in the early stages of a solution‐phase synthesis of copper nanowires, and aggregate to form the seeds from which copper nanowires grow. Removal of ethylenediamine from the synthesis leads to the rapid formation of Cu 2 O octahedra. These octahedra are introduced as seeds in the same copper nanowire synthesis to improve the yield of copper nanowires from 12% to >55%, and to enable independent control over the length of the nanowires. Transparent conducting films are made from nanowires with different lengths to examine the effect of nanowire aspect ratio on the film performance.